The invention relates to a color television transmission or information storage system, respectively, with time-division multiplex coding, the system comprising at least one data generator, at least one data receiver and a transmission or information storage channel, respectively, between the generator and the receciver, the data generator comprising at least one signal source for producing signals containing luminance, chrominance, synchronizing and identification information and an encoding circuit for time-division multiplex coding of at least a portion of said signals, which may have been subjected to a change in their time duration, the encoding circuit having an output for supplying a time-division multiplex encoded signal for transmission via the transmission channel or storage in the information storage channel, respectively, the data receiver incorporating a decoding circuit coupled to said channel and, associated with said encoding circuit, being suitable for producing signals comprising at least luminance and chrominance information which predominantly corresponds to the information produced by the signal source in the data generator, in the color television signal an image being formed from two or more fields having a predetermined number of lines. The invention also relates to a data generator and a data receiver suitable therefor.
Such a system for, more specifically, transmission is disclosed in a public report "Experimental and Development Report 118/82", published by the British "Independent Broadcasting Authority", (I.B.A.), entitled "MAC: A Television System for High-Quality Satellite Broadcasting". The report describes several variations for a MAC (Multiplexed Analog Component) picture coding. For all the variations it holds that in the data generator which constitutes the transmitter, the luminance and chrominance information are each submitted to a change in the time duration, namely a time compression, the change for the chrominance information being twice as large as the change for the luminance information. Of the chrominance information, which comprises two components per line period, one of these two components alternately occurs, time-compressed, in the time-division multiplex encoded signal. This signal contains the time-compressed luminance information associated with each line period. The picture information of each line period in the time-division multiplex encoded signal is sequentially assembled from the time-compressed luminance information and one of the two associated time-compressed chrominance information components.
In the receiver the time-division multiplex encoded signal is derived from the signal received via the transmission channel, more specifically the satellite link, and is applied to the associated decoding circuit which, with the aid of the synchronizing and identification information repeatedly produces a time decompression or expansion for the luminance and the chrominance information for the subsequent line period.
In the transmission channel, which is here, by way of example, a satellite link, there is only a limited bandwidth for the picture information transmission. Depending on the proposed variation, the report mentions bandwidths of 8.4 MHz, 7.4 MHz and 6.0 MHz. A time compression factor of 2/3 is proposed for the luminance information for the 8.4 MHz transmission channel bandwidth, so that a bandwidth of 5.6 MHz results for the bandwidth of the non-compressed luminance information. For the available picture information channel widths of 7.5 and 6.0 MHz a luminance compression factor of 3/4 is proposed, which results in values of 5.6 MHz and 4.5 MHz for the bandwidths of the non-compressed luminance information components. It was found that for the suggested variations, in view of the limited transmission channel bandwidth and the suggested structure of the time-division multiplex encoded signal to be transmitted, frequency limitations of the luminance and chrominance information are necessary.
The foregoing the description was based, by way of example, on a transmission channel in the form of a satellite link. The frequency limitations described for the transmission of information with the limited bandwidth also prevail for an information storage channel of limited bandwidth. Such a storage channel comprises information storage and display equipment such as, for example, tape and record pick-up and display devices.
The above-mentioned report describes variants of the MAC system in which time-division multiplex coding at the field frequency is applied. In one variant only the luminance information is transmitted during a number of line periods in the field period, while during further line periods only the associated time-compressed chrominance information components are transmitted. In this situation the said further line periods can be divided into two groups, one of the two chrominance information components being supplied during the first group, while the other chrominance information is supplied during the second group of line periods. The first group may occur at the beginning of the field period, whereafter the line periods containing the luminance information and thereafter the second group of line periods containing the chrominance information occur.
In still further variants one of the two chrominance information components is supplied during a number of line periods. During the line period subsequent thereto, the picture information of each line period is sequentially formed from the other chrominance information and the luminance information. Said three information components are then time-compressed. In addition, the transitions between the different types of information and consequently the time-compression factors may be variable.